minimum accurate barrel length for 7mm mauser

I just got a nicely sporterized chilean mauser in 7x57 (7mm Mauser). I'd like to shorten the barrel and stock for my wife to use it for deer/elk. what is the minimum length I should go to and still be able to get decent groups with the high twist rate barrel on it?

Some well thought of Brno rifles came with barrels that I think are a metric length that translates to 20.5". Those are nice rifles.

The barrel length, twist and accuracy don't affect each other much as long as the original twist was ok.

TurtlePhish

November 29, 2012, 11:16 PM

Length has nothing to do with accuracy as long as there's enough rifling to stabilize the bullet (which happens very quickly in the very beginning of the barrel).

What length WILL effect is how far out you'll be able to effectively reach out with the rifle.

.333 Nitro Express

November 30, 2012, 12:00 AM

Dumb question: I understand why you may want to shorten the stock (depending on your wife's length of pull), but why do you want to shorten the barrel? How long is it now?

I think that 20"-23" for a 7mm is about right--anything shorter is going to give you a lot of muzzle flash and leave a lot of powder unburned.

Art Eatman

November 30, 2012, 12:28 AM

Shorter = noiser, which makes sighting in less pleasant.

wlewisiii

November 30, 2012, 12:32 AM

I have a 19" barrel on my "scout rifle" that I am building in 7x57. I'd not be willing to go any shorter.

morcey2

November 30, 2012, 01:15 AM

Mine has a 24" barrel and I like that length. 20" is probably as short as I'd go. If I want that kind of muzzle blast, I'll grab one of my M44s or M38s. :)

Matt

lefteyedom

November 30, 2012, 01:28 AM

IMHO: 20" is a idea hunting barrel length, with an overall rifle length of not more than 40 inches.

I prefer hunting rifles to be a bit on the short side with the balance point being in the middle of the action. A rifle should look proportional and be quick to the shoulder. Muzzle blast from a 20" barrel 7X57 is very manageable. Hunting rifles are carried much and shot little. Basic marksmanship skills are best developed and maintained easy shooting rifles. Once the skills are mastered they are easily transferred to any weapon. (Savage is currently selling a HOG GUN cambered 338 Win Mag with a 20" barrel that would be almost unmanageable)

For the record:

My old Savage 110J in 7-08 has a 20" barrel with an overall length of 40". The barrel extends 10 1/2 inches past the stock, and the pull is 13". (2x7x32 burris)

My "truck gun" is an military 1898 Mauser, 8X57, its barrel is 18 1/2" with an overall length of 38". The barrel extends 8" past the stock and the pull is 13" (fix 4x scope)

MachIVshooter

November 30, 2012, 11:53 AM

I'd recommend 20"-22". The 7x57 is an efficient cartridge, but you're still burning ~50 grains of powder. Go under 20", velocity will start to suffer quite a bit, limiting range.

helotaxi

November 30, 2012, 12:15 PM

I think that 20"-23" for a 7mm is about right--anything shorter is going to ... leave a lot of powder unburned.Common misconception. The overwhelming majority of the powder that is going to burn does so before the bullet has gone 6 inches down the barrel. After that it's just a matter of the high pressure combustion products from the burned powder expanding to continue to accelerate the bullet. As long as the expanding gases still have sufficient pressure to overcome the friction of the bullet on the bore, adding barrel length will add velocity. However, you reach a point where the additional velocity gained per inch of barrel begins to drop off fairly rapidly. What barrel length that occurs at depends on the cartridge and bullet being used. The larger the ratio of powder charge to bore diameter, the longer the barrel length before this occurs. That is because the relatively large charge of powder generates a lot of gas. A lot of gas expanding down a relatively small tube creates a small expansion ratio and the result is that the pressure and resulting bullet acceleration remains fairly high for an extended distance. Cartridge that act like this are called "over-bore" though "under bore" would make more sense.

I'm not too familiar with the loading of the 7x57, but it does have a lower case capacity than the 7mm WSM. The WSM has a standard barrel length of 24" and going shorter than that starts to cost velocity quickly. The 7x57 should be somewhat less sensitive to barrel lenght within that range.

jimmyraythomason

November 30, 2012, 01:19 PM

My 7x57 performs very well with it's 20" barrel.

joed

November 30, 2012, 01:21 PM

I can understand shortening the barrel, I hated Mausers because they came with about a 40" barrel.

One thing I never see are pictures of sporterized guns, I'd like to.

rcmodel

November 30, 2012, 01:24 PM

IMO: Shortening it below 20" would be a huge mistake.

Muzzle blast will be so bad and so close to her ears your wife will hate shooting it.

rc

jimmyraythomason

November 30, 2012, 01:54 PM

One thing I never see are pictures of sporterized guns, I'd like to. Okee dokee. Here is a 7x57 built from a Chinese mauser receiver with a Latin contract barrel.

MachIVshooter

November 30, 2012, 02:41 PM

Cartridge that act like this are called "over-bore" though "under bore" would make more sense.

One has to remember that it's an abbreviated colloquialism. There's a 3rd word that gets left off most of the time: Capacity.

The correct, full term is over bore capacity

.333 Nitro Express

November 30, 2012, 04:15 PM

Helotaxi, I respectfully disagree. :)

While you are right that the bulk of the powder gets burned in the first few inches of a barrel, a shorter barrel will leave more powder unburned or not fully burned than a longer one. This is obviously more marked with slow-burning powders such as 4350, 4831 or 450, with cartridges that require a heavier charge, such as the Wby Mags, and with lower rather than higher pressures.

Here's a quote from a S.W.A.T magazine article:

According to Mike Rescigno, President of Tac Ops, the 22-inch barrel is ideal for the tactical shooters that are going to use the 190-grain Federal Match ammo. There isn't any loss of performance by going to the 22-inch barrel and this round. The Alpha 66 still provides 1/4-MOA or better accuracy.

For heavier bullets or hotter loads with slower burning powders, Rescigno recommends a 24- to 26-inch barrel. The longer barrel length is necessary for complete powder combustion with these loads. (Emphasis mine)

This also bears out with my experience working with engineers of rifle manufacturers, when we would discuss introducing a new hunting rifle in a "hot" caliber--complete combustion of slower-burning powders was always a concern.

I do agree with you that this is largely an academic discussion, though--there are a couple barrel lengths that are a commonsense minimum for standard and magnum cartridges respectively (well, depending on bore size too, but now we are wading into Megageek Land), and as long as we stay within range of these lengths, everything else is superfluous.

Please let me know if there is more recent data that shows otherwise--I'd be interested in seeing that, also because I've been out of the loop for a few years.

helotaxi

November 30, 2012, 06:25 PM

Agree or disagree, that doesn't change the internal ballistics. "Complete" powder burn is not a goal worth pursuing and any gains from a longer barrel is not because more powder burns.

Play with Quickload. Look at the percent burn number. With 3031, for example, you get a full burn almost regardless of barrel length using a 155gn pill in the .308. With Varget, almost no barrel length within reason gves you a complete burn. The velocities of the two powders track very closely through the range of barrel lengths. You'll find that the same comparison holds true with the various cartridges and powders. You'll also find that any suitable powder will be more than 90% burned in a 6" barrel and it will often take more than 30" to get 100%.

Getting all the powder to burn is a pointless exercise as the small percentage of unburned powder adds very little extra gas to the equation. It does essentially nothing to sustain the pressure curve as the pressure is dropping so fast when that last handful of percentage points of the powder charge finishes burning that measuring the difference in pressure/veloctiy from its contribution is essentially impossible because it's simply too small.

The whole point of a large case of slow powder behind a bullet isn't to provide a long duration burn, the actual difference in burn time is miniscule and measured in single digit inches of bullet travel, low single digits. What that slow powder does is slightly delay the pressure spike to control peak pressure while providing a large volume of combustion product producing a sustained pressure curve. Such cartridges benefit from a long barrel not because of the powder burning, despite what the "source" above says, but because the pressure remains high for a longer period of bullet travel. Cutting the barrel short reduces the benefit of that large powder charge and the result is that you end up with a very loud, very expensive round that does not provide any added performance over a smaller cartridge burning much less powder. You can in essence find a barrel length where a .300 WM offers no benefit over a .308 and both burn the same percentage of their powder charge, both comfortably over 90%.

Boxhead

December 1, 2012, 10:05 AM

Here's a sporter 7x57 Mauser built on a Swede (M96) action. It wears a 22" barrel and is right for this particular build.

yeah, it currently wears a 28.5" barrel, as measured from the bolt face... I don't want a barely legal rifle, i just want something handy. I read somewhere that 24" was a minimum for the 7x57 before you start losing velocity, and therefore "reach". also, tutlephish, you are right about length and accuracy, i misspoke. I think the best compromise is 22". enough to keep the balance a little forward, but short enough that it's not hanging up in the brush 3 miles ahead of you...